The present invention relates to an apparatus and method for clarifying water, and more particularly, to such an apparatus and method which cause microscopic air bubbles to attach to particles in water to be clarified so that the particles float to the surface and may be easily removed.
In a known process of removing particles from unclarified water, the unclarified water is pressurized so as to dissolve air in the water, and when the pressure is released, the dissolved air emerges as microscopic air bubbles which attach to the particles and float them on the surface for recovery. Apparatuses of the prior art for performing this process are disclosed in JP(B2) P56-23668 and its U.S. counterpart, U.S. Pat. No. 4,022,696, and Japanese Patent Pub. No. 58-23153 and its U.S. counterpart, U.S. Pat. No. 4,184,967. In these apparatuses, the unclarified water is supplied to a body of water in a flotation/separation tank within which the solids are separated.
FIG. 10 shows a typical apparatus according to the prior art including a flotation tank 1. An inlet pipe 2 opens into the tank 1 to supply thereto water which has been treated in a manner as will be explained below. A catcher pipe 3 is disposed near the bottom of the tank 1 for the discharge of clarified water. A holding tank 4 for the clarified water houses a water level pipe 5 which is connected to the catcher pipe 3. The level of the water in the pipe 5 determines the water level in the flotation tank 1.
A further tank 6 containing the original water to be clarified is connected by a pump 9 to a mixer 7. A pressurizing tank 8 holding pressurized water is connected to the mixer 7 and is connected via a pump 10 to the holding tank 4. The mixer 7 is connected to the inlet pipe 2. An air intake 11 is provided for introducing the air to the pressurizing tank 8.
A conventional skimmer rake 12 for skimming floating particles (floatables) from the surface of the water in the tank 1 is connected to the drive shaft of a motor 13. The motor 13 is mounted above the center of the tank and rotates the skimmer rake along the water's top surface. An outlet 14 is provided in the upper part of the tank 1 to discharge the particles skimmed by the skimmer rake. A second rake 15 is provided to rake sediments at the bottom of the tank 1 to an outlet 16.
In the above-described apparatus, the unclarified water to be processed, which is stored in the tank 6, is supplied by the pump 9 to the mixer 7. At the same time, a portion of the clarified water in the tank 4 is supplied by the pump 10 to the pressurizing tank 8, where the water is pressurized together with the air taken in through the intake 11, and then supplied to the mixer 7. The unclarified water reaching the mixer 7 is mixed with the pressurized water, and the mixture is fed in a pressurized condition to the inlet pipe 2.
The pressure in the tank 1 is at an atmospheric level. Thus, when the pressurized mixed water is released from the pipe 2 into the tank 1, the air dissolved in the mixed water separates from the water as microscopic air bubbles which attach themselves to the particles in the water, and the bubbles together with the attached particles float to the surface.
The particles floating on the surface in the tank 1 are skimmed off by the skimmer rake 12 which directs the particles to the outlet 14 for discharge. The remaining water in the tank 1, which is now clarified, is supplied to the tank 4 by the catcher pipe 3, from where the water is partly discharged and partly recycled to the tank 1 via the pressurizing tank 8 and the mixer 7 as described above.
In prior art water clarifying processes wherein unclarified water and pressurized water are supplied to a body of water in a tank in order that particles from the unclarified water may float to the surface and be removed, subsurface turbulence is created. Because the removal of the particles requires that they first attach themselves to microscopic bubbles to float them upward, the turbulence causes the attached bubbles and particles to firstly move downward near the bottom of the tank and then move upward to the surface. Thus, the turbulence increases the period of time required for all of the particles to float to the surface. As a result, in order to efficiently clarify a large quantity of unclarified water, a large, wide (and therefore expensive) flotation tank is required.